When a runtime is given like “mode X: 140 lm / 10 hours”. Does that mean it takes 10 hours to bring the Li-ion cell to 0 volt?
Ideally a flashlight should have low voltage protection (LVP) to prevent killing batteries. So the runtime would be how long the flashlight will give you light before the LVP kicks in (battery voltage ~2.7-2.9V).
No, it’s runtime until the flashlight turns off which does not happen at 0V, usually somewhere between 2.5 and 3V.
If a battery is drained to 0V it is permanently damaged.
You never do that to rechargeable batteries.
Example taken from Armytek Wizard Pro Nichia Magnet-USB The User Manual doesn’t specify what is runtime.
The only thing about “low voltage” is “Multicolor warning indication of low battery level and real-time temperature control”. Which I suppose means that flashlight doesn’t have LVP. I am wondering if the runtime of 10 hours, is a marketing trick. An inflate value to make it looks impressive but is impossible in reality.
Do they say to use a protected battery? One with LVP?
Here is what I read in the User Manual of the Armytek Wizard Pro Nichia
In flashlight terminology, does the above imply the flashlight will turn off at 2.5V? If so, it’s really hard to guess.
140 lumens for 10 hours sounds pretty doable. (with an 18650)
I mean, 140 lumens isn't all that bright.
Yes it does. In the modes section it tells you the lumen levels and the runtime (in days/hours/minutes)
It does. I have that light and I tested it myself.
It depends on the battery size, claimed lumen level, and runtime. 140 lumens for 10 hours on a 18650 is reasonable. Trying to accomplish the same with an AA is not.
Having no experience in light, I don’t know how to appreciate a lumen value as easily as length or weight. I don’t know how to correlate lumen to battery capacity. I want to make sure to avoid the “fine print” trap. Basically I would like to know if I run that light for 10 hours at 140 lumens. What would happen to the battery?
Providing I am using a good cell like NCR18650GA. Can you please clarify a bit? Did you mean “it is possible to get 10h from the battery at 140 lm, WITHOUT putting the battery in the danger zone?”
According to anonymous_user, the flashlight has LVP, so the battery should be safe.
Many flashlight manufacturers/sellers lie about what flashlights can do.
I don't know how truthful Armytek is.
I don't own the flashlight in question, and I haven't tested any flashlights for runtime, so I don't know what the real runtime is.
The easiest way is to have an existing flashlight with realistic lumen levels and using that to compare.
Wait for other people to test/review it and see what they find.
The battery will be low and you will need to charge it.
Either the battery or flashlight can have low voltage protection. If a device is draining the battery voltage to dangerous levels then that means you are using an unprotected cell in a flashlight without LVP (or the protection in either item failed).
Oh what a relief thanks. Why would the manufacturer not mention such a critical feature in the product description (auto cutoff when battery voltage is low).
I saw that too of course, and it is still confusing. Hence the question in this thread. Runtime X until the battery is dead or until the flashlight turns off the battery at cutoff voltage is two totally different kinds of runtime. I am used to the alkaline batteries, so the runtime until the battery is dead seems the most natural definition.
Well unless you plan on using unprotected batteries in flashlights without LVP, then runtime until the battery is dead dead is not that useful.
First alkaline batteries are non-rechargable and due to the different chemistry don’t have the same issues as a lithium-ion. Secondly if your flashlight (or other device) drains an alkaline until shutoff that doesn’t mean the battery will be at 0V. Some devices can operate with lower voltages than others.
Excerpted from the user manual :
So the given runtime corresponds to the consumption of 90% of 3500 mAh = 3150 mAh?
I assume in Li-ion battery, when the capacity reaches 10% remaining, this is where the cell reaches its cutoff voltage 2.7V and the Low Voltage Protection of the flashlight will kick in, right?
If it says, "140 lumens for 10 hours" then after 10 hours, the light output will be at 14 lumens.
It is difficult to tell how much of 3500 mAh will be used without testing it.
Runtime in hours is basically the battery capacity in Mah’s divide by the current drawn in milliamps measured at the tail.
If your using a 3500 mah battery and your drawing 1000 ma of current then that equates to roughly 3.5 hours of runtime.
3500 / 1000 = 3.5
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Another way that I get a estimate of run time is to look at the led im using in some of the led test that’s been done by forum members here.
Those graph’s give you a idea of lumens per current and the vf at that current.
If you know the current its using and the led used it gives you a close estimate of lumens.
HKJ’s battery graphs is also a important part of getting a good estimate of run time.
This gives me a close estimate before I even start to build a light.
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With NIB lights, sometimes they can be very misleading or just a made up number. Usually the more expensive well known brands are pretty honest.
But even then, they may have hand picked the led for output and tested the highest capacity battery available, then hand picked the best one for the run time test.
So the number they give can be really achieved if ever thing is just right. Some use a middle of the road number, you may get a light than can produce more lumens than whats on the box or you could be slightly lower. A lot of factors contribute to more or less lumens, especially in a factory setting. I must admit though that some of the companys we deal with here being budget minded have been producing some very honest numbers lately.
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Leds have a rating for a certain amount of current in versus how many lumens out and they are binned that way. But the rating may be 160 to 200 lumens at 350 ma in a certain bin. So if its driven at 700 ma that’s roughly 320 to 400 lumens in that bin. The led Lottery. Two light’s of the same make and model made on the same day could have a difference of 80 lumens at 700 ma. They could even switch bins of a led in mid production because they rain out of the original. There not going to remake the box to reflect that though.
These are just numbers I made up but it shows one difference just in the luck of the draw with the led. The driver and how efficient it is and type of driver is whole nother can of worms.
Just my two cents 
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16 posts in and nobody has mentioned the FL1 standard?
Most flashlight manufacturers advertise according to the FL1 standard, in which output is measured at 30 seconds, and runtime is until the output is 10% of that. There’s a lot you could want to know about a light’s behavior as the battery drains the FL1 standard doesn’t cover. You’ll need to read reviews that have runtime graphs to know how it behaves.
I reviewed the Wizard Pro 144A. My very early sample did not have low-voltage protection, but production examples sold by Armytek itself and Killzone Flashlights do. Aside from thermal-throttling and LVP, output is stable as the battery drains, while in many flashlights, there’s a large difference between the time to 80% and the time to 10%. Except in the top two modes, which may thermal throttle, those two numbers are the same with the Wizard Pro.
lights that are designed for NON-rechargeables, though, actually SHOULD run them to zero
i had an XTAR WK42 that would figure out when a new battery was installed, whether it was rechargeable, or not
(it took 16340 li, or CR123 lithium primaries)
based on that (initial volts are different), then it would either stop at 3V, or 0V.
Here is an interesting article about big name brand headlamp makers and why basically nothing they say about brightness and runtime can be trusted.
And yet many flashlight makers are quite truthful about brightness and runtimes.
Many of our members post runtime plots that show exactally what you can expect during a full run.
All the Best,
Jeff
ANSI runtimes (what many of the brands trusted and respected by us use) are the time to 10% of the brightness measured at 30 seconds after activation for each mode. Not until the light shuts off, and not until the emitter is barely glowing. So at 1000 lumens, until it drops to <100, and for a 20 lumen mode until it drops to <2.
More on ANSI standards here